Gas-tight syringes

Gas-tight syringes, equipped with valves, 50- to 1000- xL (Supelco). 

Weigh 50 g of sample into the headspace flask with a magnetic stirrer bar. Add immediately 50 mL of 1.5% stannous chloride solution in hydrochloric acid, and close the vessel with the silicone-rubber septum and the screw-cap. Transfer the head-space flasks into the electric oven (or water-bath) heated at 80 °C for 1 h. After 15 min, take the flasks out of the oven and mix the contents with the magnetic stirrer, heated at 50 °C, for 1 min. Return the flasks to the electric oven and repeat the mixing of the samples every 15 min. After 1 h, take the flasks out of the oven, mix the contents of each flask for 1 min, and inject an aliquot of headspace (100-1000 xL) on to the GC column with a gas-tight syringe. 

Saliva Collect 3 mL aliquot with sterile pipette introduce into 2-ounce glass container and cap incubate 24 hours at 37°C withdraw through cap with gas-tight syringe. GC/FID, microcoul-ometric tritration NR NR Solis and Volpe 1973... 

The gaseous atmosphere was then vented through a trap at -78° (to remove most of the benzene vapor) into an evacuated vessel. Samples were removed by gas-tight syringe and injected into a Hewlett-Packard 5790 gas chromatograph, equipped with a U ft, 1/8 in Porapak P column and a flame ionization detector. Use of known samples of hydrocarbons (methane and ethane) established that the minimum detectable amounts of product by this procedure were about 0.5-1 0 % (based on starting Nb complex). Several of the reactions (Mo(CO)g, W(C0)g and Ru (CO) p) gave small amounts (around 1-2 %) of these alkanes only with Cr(C0)g was a substantial yield of hydrocarbon product consistently observed (see below). 

Although it is possible to carry out the cleavage of the resins directly on the Nautilus, the delivery of the HMDS standard solution is not sufficiently accurate to allow determination of loadings by H NMR. After removal of the vessels from the reaction module, 1.00 mL of the HMDS solution was carefully added by gas tight syringe. 

The second alt ernative uses a gas-tight syringe with a valve closure, is equally convenient, and does not require the creation of a positive pressure in the sample container. In this case, it is desirable once again to use a standard glass syringe but with a valve at the end. The syringe chosen should be larger than the... 

When the scattering cell has been purified with accuracy, the arrangement can be simplified by directly connecting a gas-tight syringe with a filtration holder to the scattering cell (Fig. 10). 

Injector, 250°C 10-ml gas-tight syringe 100-ml flask fitted with a rubber septum... 

Withdraw 5 ml headspace gas from above the essence sample into a 10-ml gas-tight syringe. Inject slowly into the GC. 

Because SPME extracts compounds selectively, the response to each compound must be calibrated for quantification. A specific compound can be quantified by using three GC peak area values from solvent injection, static headspace (gas-tight syringe), and SPME. The solvent injection is used to quantify the GC peak area response of a compound. This is used to quantify the amount of the compound in the headspace. The SPME response is then compared to the quantified static headspace extraction. These three stages are necessary because a known gas-phase concentration of most aroma compounds at low levels is not readily produced. A headspace of unknown concentration is thus produced and quantified with the solvent injection. Calibration must be conducted independently for each fiber and must include each compound to be quantified. 

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